Do not evaluate variadic template types

This is a workaround for an internal clang assertion that gets triggered
if we try to evaluate a variadic template type reference.

Fixes rust-lang#283

Author: fitzgen

libbindgen/src/clang.rs

@@ -487,7 +487,7 @@ impl Cursor {
     }
 
     /// Try to evaluate this cursor.
-    pub fn evaluate(&self) -> EvalResult {
+    pub fn evaluate(&self) -> Option<EvalResult> {
         EvalResult::new(*self)
     }
 }
@@ -1306,10 +1306,31 @@ impl EvalResult {
 #[cfg(not(feature = "llvm_stable"))]
 impl EvalResult {
     /// Evaluate `cursor` and return the result.
-    pub fn new(cursor: Cursor) -> Self {
-        EvalResult {
-            x: unsafe { clang_Cursor_Evaluate(cursor.x) },
+    pub fn new(cursor: Cursor) -> Option<Self> {
+        // Clang has an internal assertion we can trigger if we try to evaluate
+        // a cursor containing a variadic template type reference. Triggering
+        // the assertion aborts the process, and we don't want that. Clang
+        // *also* doesn't expose any API for finding variadic vs non-variadic
+        // template type references, let alone whether a type referenced is a
+        // template type, instead they seem to show up as type references to an
+        // unexposed type. Our solution is to just flat out ban all
+        // `CXType_Unexposed` from evaluation.
+        let mut found_cant_eval = false;
+        cursor.visit(|c| {
+            if c.kind() == CXCursor_TypeRef && c.cur_type().kind() == CXType_Unexposed {
+                found_cant_eval = true;
+                CXChildVisit_Break
+            } else {
+                CXChildVisit_Recurse
+            }
+        });
+        if found_cant_eval {
+            return None;
         }
+
+        Some(EvalResult {
+            x: unsafe { clang_Cursor_Evaluate(cursor.x) },
+        })
     }
 
     fn kind(&self) -> Enum_CXEvalResultKind {

libbindgen/src/ir/var.rs

@@ -209,8 +209,9 @@ impl ClangSubItemParser for Var {
                         _ => unreachable!(),
                     };
 
-                    let mut val =
-                        cursor.evaluate().as_int().map(|val| val as i64);
+                    let mut val = cursor.evaluate()
+                        .and_then(|v| v.as_int())
+                        .map(|val| val as i64);
                     if val.is_none() || !kind.signedness_matches(val.unwrap()) {
                         let tu = ctx.translation_unit();
                         val = get_integer_literal_from_cursor(&cursor, tu);
@@ -225,7 +226,7 @@ impl ClangSubItemParser for Var {
                     })
                 } else if is_float {
                     cursor.evaluate()
-                        .as_double()
+                        .and_then(|v| v.as_double())
                         .map(VarType::Float)
                 } else {
                     None

libbindgen/tests/expectations/tests/eval-variadic-template-parameter.rs

@@ -0,0 +1,12 @@
+/* automatically generated by rust-bindgen */
+
+
+#![allow(non_snake_case)]
+
+
+#[repr(C)]
+#[derive(Debug, Copy, Clone)]
+pub struct B<T> {
+    pub _address: u8,
+    pub _phantom_0: ::std::marker::PhantomData<T>,
+}

libbindgen/tests/headers/eval-variadic-template-parameter.hpp

@@ -0,0 +1,8 @@
+// bindgen-flags: -- -std=c++11
+
+template <typename... T>
+struct B {
+    // Can't generate anything meaningful in Rust for this, but we shouldn't
+    // trigger an assertion inside Clang.
+    static const long c = sizeof...(T);
+};